1. Field of the Invention
The present invention relates to a fault detecting system for a computer network in which a plurality of computer systems placed in a wide area or on the premises is interconnected, and more particularly relates to a fault detecting system which effectively detects faults occurring in a high-speed communication network.
2. Related Background Art
A conventional computer network system as shown in a typical example of FIG. 7 has a system confirmation that computer systems which are placed in business offices A, B, C and D which are regionally apart, are interconnected by high-speed digital network lines S1, S2 and S3.
Further, in a case that the computer system of the business office A2 is centralized to monitor faults on the computer network system, the computer system of the business office A comprises a host computer 1, a communication control unit 2, a network control host 3, and a time-division multiplexer 4, and the other offices B, C and D comprise time-division multiplexers 5, 6 and 7, communication control units 8, 9 and. 10, and host computers 11, 12 and 13. The time-division multiplexers 4, 5, 6 and 7 are interconnected by the high-speed digital network lines S1, S2 and S3. Then, the network control host 3 of the business office A is centralized to monitor whether a fault occurs in the network.
Here, in general, a form of the network includes a direct connection such that the business office A and the business office B are directly connected by the high-speed digital network line S1 or the business office A and the business office D are directly connected by the high-speed digital network line S3 and an indirect connection such that the business office A and the business office C are connected by the high-speed digital network lines S1 and S2 though the time-division multiplexer 5.
Next, the functions of the network control host 3 will be described in detail. For example, in a case that a fault occurs on the high-speed digital network line S1 which directly connects the business offices A and B, communication between the units 4 and 5 is disable, and then the network control host 3 receives a fault occurring report from the time-division multiplexer 4 and make a display unit 3D display an alarm indication. Next, a maintenance person (operator), who suspects this indication, inputs a control request command and receives the fault condition information from the time-division multiplexer 4 in order to judge whether the fault is a perpetual fault or an instantaneous fault such that a system power supply instantaneously falls. Then, when the maintenance person confirms the perpetual fault, the maintenance person inputs a request command to reconnect the high-speed digital network line S1 from the network control host 3, so that communication between the business office A and the business office B is restored.
In a case that a fault occurs on the high-speed digital network line S3 which directly connects the business offices A and D, the same restoring process is performed.
On the other hand, in a case that a fault occurs on the high-speed digital network line S2 which is a network form of indirectly connecting the business office C with the business office A trough the business office B, the time-division multiplexer 5 of the business office B detects that communication with the time-division multiplexer 6 of the business office C on the lower part is disable, and sends the fault occurring report to the time-division multiplexer 4 of the business office A. Then, the network control host 3 receives the fault occurring report and makes the display unit 3D display the alarm indication. Next, a maintenance person who suspects this indication inputs a control request command from the network control host 3 and receives the fault condition information from the time-division multiplexer 5 in order to judge whether the fault is a perpetual fault or a instantaneous fault such that a system power supply instantaneously falls. Then, when the maintenance person confirms the perpetual fault, the maintenance person inputs a request command to reconnect the high-speed digital network line S2 from the network control host 3, so that communication between the business office B and the business office C is restored. Consequently, the network form of the business office A and the business office C, which are indirectly connected, is restored.
Note that as the conventional technique, Japanese Patent Laid-Open No. 1-26956 (26956/1989) "Intermittent Fault Detecting Method" has been known.
However, such a conventional fault detecting system for the computer network had the following problems.
The first problem was that whether the fault of the high-speed digital network line was a perpetual fault (serious fault) or an instantaneous fault (slight and self restoring fault) such that a system power supply instantaneously fell, the aforesaid network control host displayed the indication of-the fault occurring on the display unit without considering the seriousness of the fault. In particular, there is a case that such a slight fault occurs few times a day whereas a perpetual fault rarely occurs few times a year. Accordingly, the problem arose that the maintenance person got used to the slight fault on ordinary work, consequently the maintenance person failed to notice the serious faults. Moreover, in order to avoid such mistakes on maintenance, the control request command was inputted to confirm the condition of faults for all cases regardless of the seriousness of the faults, and then the restoring process was performed after the condition of the faults was confirmed; however, these processes were complicated and in particular, in a case of monitoring a computer network having the large number of computer systems, the maintenance person had to take care of enormous fault occurring reports.
The second problem was that in a case of a form of the indirect connection such that the business offices A and C were indirectly connected though the business office B as shown in FIG. 7, for example when the fault occurred on the high-speed digital network line S2 on the lower side, the following problem arose. The problem will be described in detail by comparing the condition of the high-speed digital network line S2 with each processing state of the business offices A, B and C.
Referring to FIG. 8, assuming that a fault occurs on the high-speed digital network line S2 at some point t.sub.1, the time-division multiplexers 5 and 6 of the business offices B and C detect the fault (at the point of t.sub.2).
Next, the time-division multiplexer 5 of the business office B issues the fault information E.sub.BA indicating the occurrence of the fault (at the point of t.sub.3), and further the occurrence of the fault is reported to the network control host 3 by transmitting the fault information E.sub.BA to the time-division multiplexer 4 of the business office A through the line S1 (at the point of t.sub.4). On the other hand, the time-division multiplexer 6 of the business office C also issues the fault information E.sub.CB (at the point of t.sub.3) and tries to transmit the information E.sub.CB to the time-division multiplexer 5 of the business office B. In other words, the time-division multiplexer 6 tries to indirectly transmit the fault information E.sub.CB to the time-division multiplexer 4 of the business office A through the time-division multiplexer 5. However, since there is a fault on the high-speed digital network line S2, actually the fault information E.sub.CB is not transmitted. Consequently, the time-division multiplexer 6 continues to issue the fault information E.sub.CB until the acknowledgement information is sent back from the time-division multiplexer 5.
Next, once the network control host 3 of the business office A receives the fault information E.sub.BA (at the point of t.sub.5), this information is reported to the maintenance person by the alarm display on the display unit 3D (at the point of t.sub.6).
Next, when reacting to the alarm display, the maintenance person instructs to restore the fault (at the point of t.sub.7), the network control host 3 transmits the restoration information R.sub.AB to the business office B (at the point of t.sub.8). Then, the computer system of the business office B receives this restoration information R.sub.AB (at the point of t.sub.9), and the high-speed digital network line S2 is treated to restore. When the restoration is completed (at the point of t.sub.10), a completion report is transmitted to the network control host 3 of the business office A from the business office B and is displayed on the display unit 3D. Accordingly, the maintenance person can confirm the restoration of the high-speed digital network line S2.
On the other hand, as described above, the time-division multiplexer 6 of the business office C continues to issue the fault information E.sub.CB until the high-speed digital network line S2 is restored (until at the point of t.sub.3 or at the point of t.sub.10), and at the point (t.sub.11) after the restoration is completed (at the point of t.sub.10), finally the time-division multiplexer 6 can transmit the fault information E.sub.CB to the time-division multiplexer 5 of the business office B. Next, when the time-division multiplexer 5 receives this information E.sub.CB (at the point of t.sub.12), it transmits this information E.sub.CB to the time-division multiplexer 4 (at the point of t.sub.13). Next, when the time-division multiplexer 4 receives the fault information E.sub.CB (at the point of t.sub.14), it instructs the display unit 3D to display that the fault occurs on the high-speed digital network line S2.
It is apparent from the explanation, the fault information E.sub.BA and the fault information E.sub.CB indicate the same fault on the high-speed digital network line S2. Then, reacting to the fault information E.sub.BA, the network control host 3 performs restoring, and even though the restoration of the fault is completed at the point (t.sub.10), the display unit 3D displays again that the fault occurs based on the fault information E.sub.CB delayed in transmitting. However, the maintenance person could not notice the identity of the alarm display based on the fault information E.sub.CB and the fault information E.sub.BA, so that some irrationality was caused such that the maintenance person considered that the alarm display based on the fault information E.sub.CB was the occurrence of a new fault and then instructed again to restore the high-speed digital network line S2.